The current art for obtaining a total prostheses for the maxillary arch or for the mandibular arch essentially comprises four phases that precede the actual construction phase of the prosthesis.
The first phase entails obtaining a negative primary print of the edentulous arch to be fitted with a prosthesis. For this phase, a standard print holder is used, which is available in different sizes and coarsely fits on the arch to be provided with a prosthesis. The print holder is filled with suitable material, for instance alginate, it is positioned on the arch and the so-called negative primary print of the arch is obtained.
In the course of the second phase, a primary model of the edentulous arch is obtained. The negative primary print of the arch is filled with appropriate material, for instance plaster, and after it has dried the so-called positive primary print of the arch is realised.
From the third phase, an individual negative secondary print holder is obtained. This print holder is individual because it is specific and personalized for the patient. On the positive primary model of the arch some preparatory interventions are performed, such as contouring the primary model, in order to obtain an individual print holder that takes into account the anatomic specificity of each individual patient.
Upon completion of these preparatory interventions the positive primary model of the arch is coated with suitable dental material, generally waxy material, to create a certain thickness with respect to the arch, and subsequently it is coated with other dental material, generally acrylic resin. When the resin is polymerised the positive primary model is removed and a negative print of the arch is obtained, which constitutes an individual secondary print holder of the arch.
The fourth phase allows to obtain a final positive model of the arch whereon the prosthesis is to be constructed.
The secondary individual print holder is subjected to border moulding, i.e. the rim of the individual print holder is coated with essentially resinous and/or waxy material, and the print holder thus coated is inserted on the arch to be fitted with a prosthesis in the mouth of the patient, who is requested to perform the functional movements that leave trace on the part of the rim of the print holder whereon material has been placed which, having certain malleability characteristics, records aggregations, separations projections etc., due to the movement of the muscles of the patient's mouth. Upon completion of this operation the individual print completed by the border moulding is "cleaned" and different dental material, for instance polysulphur, is inserted which, adhering to the negative of the individual print holder generates the negative of the individual secondary print. Then, with special dental material, generally high precision plaster, the positive and definitive secondary model that serves as the base for the realization of the prosthesis is realized.
Hence, the traditional procedure is long and relatively costly in that it entails obtaining the prints of the arches twice and it generally calls for the realization of an individual print holder in the laboratory. Moreover, obtaining the primary prints with standard print holders may cause discomfort to the patient.